net: phy: sfp: remove sfp_mutex's definition

The sfp_mutex variable is defined but never used in this file. Not even
in the commit that introduced that variable.

Remove sfp_mutex, it has no purpose.

Cc: Andrew Lunn <andrew@lunn.ch>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: NSebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: NAndrew Lunn <andrew@lunn.ch>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/phy/sfp.c

@@ -163,8 +163,6 @@ static const enum gpiod_flags gpio_flags[] = {
 /* Give this long for the PHY to reset. */
 #define T_PHY_RESET_MS	50
 
-static DEFINE_MUTEX(sfp_mutex);
-
 struct sff_data {
 	unsigned int gpios;
 	bool (*module_supported)(const struct sfp_eeprom_id *id);